A federal grand jury charged a 64-year-old man from Ireland Capital city Dublin for emailing more than 40 bomb threats to the University of Pittsburgh, three federal court houses and a federal officer earlier this year, reports Pittsburgh Post-Gazette.

Adam Stuart Busby -who is under arrest in Ireland on an unrelated charge -was charged with 17 counts of wire fraud, 16 counts of maliciously conveying false information and two counts of international extortion.

He has also been charged with threatening US Attorney David Hickton, CNN reported.

His consistent threatening emails had resulted in more than 100 school evacuations, officials said.

The series of threats spanned March 30 through April 21 and these emails were 'an understandable source of heightened anxiety,' said University Chancellor Mark Nordenberg. After receiving 10 bomb threats in three weeks in the month of April, the school offered a $50,000 reward for information leading to the capture of whoever was responsible.

The threats were investigated by the Department of Justice, the FBI and the University of Pittsburgh police.

According to the Irish Times newspaper report of July 2010, Busby was convicted of emailing two false bomb threats in 2006 to Heathrow Airport in London. Those threats, which cited specific international flights, claimed to be from the Scottish National Liberation Army, according to the Times.

Busby who is Scottish by birth, first went to Ireland in 1980 after facing charges in his native country of criminal damage to property of the English ministry of defence, according to the Times. Also, He has been diagnosed with multiple sclerosis and uses a wheelchair.

In a related indictment, two Ohio men, Alexander Waterland, 24, and Brett Hudson, 26 were charged with making additional threats against the university. They were identified as members of computer hacking group Anonymous.

Altogether, the university has received 143 threats this year. The first was made on Feb. 13 against the University's Chevron Science Centre, where the chemistry department is located.